A large number of biologically important proteins, such as hormones, enzymes and cell surface receptors undergo early steps of their biogenesis in the endoplasmic reticulum (ER). Defects and variations in efficiency of this process are believed to contribute to important human diseases. For example, misfolding and degradation accounts for lack of enzymes in lysosomal storage diseases or membrane transporters in certain kidney diseases. The protein folding environment in the ER is regulated by signal transduction pathways that together constitute the ER unfolded protein response (UPR), which responds to misfolded protein stress in the organelle. Relatively crude genetic manipulation of these pathways has shown that modulating the protein folding environment in the ER can have important pathophysiological consequences: For example, evidence suggests that loosening the quality control in the ER might allow mildly misfolded proteins that are otherwise functional to escape ER retention and degradation and contribute to essential cellular functions and thereby ameliorate severe phenotypes of loss-of-function mutations. Other studies show that cancer cells from human tumors are particularly reliant on their UPR for survival, suggesting that UPR inhibitors may have selective toxicity against cancer. Therefore, availability of pharmacological probes to modulate signaling in the UPR will provide much needed tools to test the suitability of the pathway as a target for therapeutic intervention in diseases of protein misfolding and cancer. Phosphorylation of translation initiation factor 2a (eIF2a) by the ER stress activated protein kinase PERK is a well understood and potentially malleable arm of the UPR that is referred to as the integrated stress response (ISR). Robust cell-based assays for activity of the ISR have been developed. These entail measurements of the magnitude of translation repression attendant upon PERK activation and eIF2a phosphorylation and a complementary assay that reports on the activity of the gene expression program that is initiated by eIF2a phosphorylation. The assays in question have been miniaturized and converted to a homogenous format suitable for high throughput screens (HTS) for small molecules ("probes") that when added to cells, would either block PERK activity, impair the downstream steps required for eIF2a phosphorylation or the conversion eIF2a phosphorylation signal to the activation of gene expression. Tertiary assays have been developed to pinpoint the site of action of any inhibitory molecules discovered by the HTS. An HTS campaign using these assays is expected to yield potent cell penetrant small molecules that inhibit the ISR at various points in vivo. Unlike the genetic approaches, which tend to produce relatively discontinuous dose responses, small molecule inhibitors are predicted to have continuous dose-response relationships with lengthy monotonic phases. These feature will be exploited by the research community to test the hypothesis that gentle and partial inhibition of the ISR might promote the secretion of otherwise misfolded proteins and selectively compromise the viability of tumor models. Our understanding of the processes by which proteins attain their proper structure has increased markedly in recent years and with that understanding come the prospects of intervening in the process of protein folding to therapeutic ends. This study focuses on one pathway by which cells regulate their capacity to fold proteins in the secretory compartment and is designed to identify drug-like compounds that modulate signaling in that pathway by inhibiting one of its key components, an enzyme called PERK. If successful, this study will tell us whether or not PERK inhibitors have potential utility in treating diseases of protein misfolding, such as lysosomal storage diseases and various cancers. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]